Plug valve having preloaded seal segments

ABSTRACT

A plug valve including a valve body having an inlet port, an outlet port and a central chamber extending between the inlet port and the outlet port. The valve also includes an inlet seal segment within the central chamber and includes a bore extending therethrough and aligned with the inlet port. An outlet seal segment is disposed within the central chamber having a bore extending therethrough and aligned with the outlet port. A plug member is disposed in the central chamber and is moveable between an open position, to facilitate fluid flow through the plug valve, and a closed position, to block fluid flow through the plug valve. First and second side segments are disposed between and interlocked to the inlet and outlet seal segments to encircle the plug member. The side segments are tensioned to preload the seal segments against the plug member to prevent the flow of fluid between the seal segments and the plug member.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application No. 61/684,008 filed on Aug. 16, 2012, which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

This disclosure relates to plug valves, and more particularly, to a seal assembly for plug valves, and even more particularly, to a preloaded seal assembly for plug valves.

BACKGROUND OF THE DISCLOSURE

Plug valves typically include a body having an inlet port, an outlet port and a central chamber extending between the inlet and outlet ports. A plug member is rotatably positioned inside the central chamber sandwiched between an upstream seal segment and a downstream seal segment. Each seal segment includes a through bore that is aligned with the respective inlet and outlet ports to form a flow passage through the plug valve body. The plug member also includes a central bore extending therethrough such that during operation, the plug member rotates between an open position, to align the central bore with the flow passage to facilitate fluid flow through the plug valve, and a closed position, to offset the central bore from the flow passage to block fluid flow through the plug valve.

Plug valves are designed so that the plug member shifts or otherwise “drifts” small amounts in the axial direction relative to the flow of fluid. This drift oftentimes enables fluid particulate to migrate between the plug member and the seal segments. For example, when the plug valve is in a closed position, the plug member drifts apart from the upstream seal segment causing a gap to form between an inner surface of the inlet seal segment and an outer surface of the plug member. As a result, fluid and other fine particles such as, for example, frac sand, that flow through the plug valve will migrate between the seal segment and the plug member, which can accumulate, causing an increase in friction or imbed therebetween, which ultimately diminishes seal performance.

SUMMARY

In a first aspect, there is provided a plug valve including a valve body having an inlet port, an outlet port and a central chamber extending between the inlet port and the outlet port. An inlet seal segment is disposed within the central chamber and has a bore extending therethrough and aligned with the inlet port. An outlet seal segment is disposed within the central chamber and has a bore extending therethrough and aligned with the outlet port. A plug member is disposed in the central chamber and is moveable between an open position, to facilitate fluid flow through the plug valve, and a closed position, to block fluid flow through the plug valve. First and second side segments are disposed between and interlocked to the inlet and outlet seal segments to encircle the plug member. The side segments are tensioned to preload the seal segments against the plug member to prevent the flow of fluid between the seal segments and the plug member.

In certain embodiments, the inlet and outlet seal segments each include a pair of recesses disposed on an outer face and are configured to receive corresponding extensions on an inner face of the first and second side segments to interlock the seal segments and the side segments together.

In other certain embodiments, the first and second side segments include a pair of recesses disposed on an inner face and are configured to receive corresponding extensions on an outer face of the inlet and outlet seal segments.

In yet another embodiment, the first and second side segments are formed of urethane.

In still another embodiment, the first and second side segments include an inner arcuate surface, wherein a central section of the inner arcuate surface is spaced apart from the plug member to reduce friction between the plug member and the first and second side sections during movement of the plug member between the open and closed positions.

In another embodiment, the first and second side segments and the inlet and outlet seal segments form an inner diameter that is sized smaller than an outer diameter of the plug member such that when the seal segments and side segments encircle the plug member, the side segments are tensioned to preload the seal segments against the plug member.

In still another embodiment, the preload force is between about 445 N (100 lbf) to about 5338 N (1200 lbf)

In still another embodiment, the preload force is between about 445 N (100 lbf) to about 2002 N (450 lbf).

In yet another embodiment, the preload force is between about 667 N (150 lbf) to about 1780 N (400 lbf).

In still another embodiment, the preload force is between about 1112 N (250 lbf) to about 1557 N (350 lbf).

In a second aspect, there is provided a plug valve including a valve body that has an inlet port, an outlet port and a central chamber extending between the inlet port and the outlet port. An inlet and an outlet seal segment are disposed within the central chamber proximate the inlet and outlet ports, respectively. Each inlet and outlet seal segment has a bore extending therethrough and coaxially aligned with valve body inlet and outlet ports. A plug member is disposed in the central chamber and is moveable between an open position to facilitate fluid flow through the plug valve, and a closed position to block fluid flow through the plug valve. At least one side segment has ends that are nestable with respective ends of the inlet and outlet seal segments to interlock the at least one side segment to the inlet and outlet seal segments. The at least one side segment and the seal segments are sized to encircle the plug member such that the at least one side segment is tensioned to preload the seal members against the plug to form a seal between the plug and the seal segments to prevent the flow of fluid between the seal segments and the plug member.

In certain embodiments, the at least one side segment includes a pair of side segments that have ends nestable with respective ends of the inlet and outlet seal segments to interlock the side segments to the inlet and outlet seal segments.

In other certain embodiments, the inlet and outlet seal segments each include a pair of recesses disposed on an outer face that are configured to receive corresponding extensions on an inner face of the at least one side segment to interlock the seal segments and the at least one side segment together.

In yet another embodiment, the first and second side segments include a pair of recesses disposed on an inner face to receive corresponding extensions on an outer face of the inlet and outlet seal segments.

In still another embodiment, the at least one side segment is formed of urethane.

In yet another embodiment, the at least one side segment is tensioned to pull the seal members against the plug with a force of between about 445 N (100 lbf) to about 5338 N (1200 lbf).

In yet another embodiment, the at least one side segment includes an inner arcuate surface, wherein a central section of the inner arcuate surface is spaced apart from the plug member to form a gap between the at least one side segment and the plug member to reduce friction between the plug member and the at least one side segment during movement of the plug member between the open and closed positions.

In still another embodiment, the at least one side segment and the inlet and outlet seal segments form an inner diameter that is sized smaller than an outer diameter of the plug member such that when the at least one seal side segment and the inlet and outlet seal segments encircle the plug member, the at least one side segment is tensioned to preload the seal segments against the plug member.

In a third aspect, a method of manufacturing a plug valve includes forming a valve body that has an inlet port, an outlet port and a central chamber extending between the inlet port and the outlet port. An inlet seal segment and an outlet seal segment are inserted within the central chamber proximate the inlet and outlet ports, respectively, such that respective bores extending through the inlet and outlet ports are coaxially aligned with valve body inlet and outlet ports. At least one side segment is inserted between respective ends of the inlet and outlet seal segments. The at least one side segment has ends nestable with respective ends of the inlet and outlet seal segments to interlock the at least one side segment to the inlet and outlet seal segments. The at least one side segment and the seal segments are configured to encircle and otherwise form a plug receiving area having an inner diameter. At least one side segment is tensioned by inserting a plug member that has an outer diameter sized larger than the receiving area inner diameter to create a pulling force and thereby preload the inlet and outlet seal members against the plug to form a seal between the plug and the seal segments.

In certain embodiments, inserting the at least one side segment includes inserting a pair of side segments having ends nestable with respective ends of the inlet and outlet seal segments to interlock the side segments to the inlet and outlet seal segments.

In other certain embodiments, extensions are formed on an inner face of the pair of side segments, and a pair of recesses are formed on an outer face of the inlet and outlet seal segments to receive corresponding extensions on the pair of side segments. The extensions on the side segments are inserted in the recesses on the seal segments to interlock the seal segments and side segments together.

In yet another embodiment, recesses are formed on the pair of side segments, and extensions are formed on an outer face of the inlet and outlet seal segments for insertion into respective recesses on the pair of side segments. The extensions are inserted in the recesses to interlock the seal segments and side segments together.

In still another embodiment, the at least one side segment is formed of urethane.

In yet another embodiment, the plug member diameter is formed to a size sufficient to tension the at least one side segment to pull the seal members against the plug member with a force of between about 445 N (100 lbf) to about 5338 N (1200 lbf).

In still another embodiment, the at least one side segment is formed to include an inner arcuate surface, wherein a central section of the inner arcuate surface is spaced apart from the plug member to form a gap between the at least one side segment and the plug member to reduce friction between the plug member and the at least one side segment during movement of the plug member between open and closed positions.

In a fourth aspect, a seal assembly for a plug valve that includes a valve body that has an inlet port, an outlet port and a central chamber extending between the inlet port and the outlet port. A plug member is disposed in the central chamber and is moveable between an open position, to facilitate fluid flow through the plug valve, and a closed position, to block fluid flow through the plug valve. The seal assembly includes an inlet seal segment that is disposed within the central chamber and has a bore extending therethrough that is aligned with the inlet port. An outlet seal segment is disposed within the central chamber and has a bore extending therethrough that is aligned with the outlet port. First and second side segments have ends nestable with and interlocking to respective ends of the inlet and outlet seal segments for encircling the plug member and tensioning the side segments to pull the seal members against the plug to form a seal between the plug and the seal segments.

In certain embodiments, the first and second side segments are formed of urethane.

In other certain embodiments, the inlet and outlet seal segments each include a pair of recesses disposed on an outer face and are configured to receive corresponding extensions on an inner face of the first and second side segments to interlock the seal segments and the side segments together.

In yet another embodiment, the first and second side segments include a pair of recesses disposed on an inner face and are configured to receive corresponding extensions on an outer face of the inlet and outlet seal segments to secure the seal segment and the side segments together.

In still another embodiment, the first and second side segments include an inner arcuate surface, wherein a central section of the inner arcuate surface is spaced apart from the plug member to reduce friction between the plug member and the first and second side sections during movement of the plug member between the open and closed positions.

In yet another embodiment, the first and second side segments and the inlet and outlet seal segments form an inner diameter that is sized smaller than an outer diameter of the plug member such that when the seal segments and side segments encircle the plug member, the side segments are tensioned to preload the seal segments against the plug member.

In still another embodiment, the preload force is between about 445 N (100 lbf) to about 5338 N (1200 lbf).

Other aspects, features, and advantages will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, which are a part of this disclosure and which illustrate, by way of example, principles of the inventions disclosed.

DESCRIPTION OF THE FIGURES

The accompanying drawings facilitate an understanding of the various embodiments.

FIG. 1 is a section view of a plug valve having a preloaded seal assembly.

FIG. 2 is a section view of the plug valve of FIG. 1 taken along the line 2-2.

FIG. 3 is an exploded perspective view of the seal assembly of FIGS. 1 and 2.

FIG. 4 is a section view of an alternate configuration of the seal assembly.

FIG. 5 is an exploded perspective view of the seal assembly of FIG. 4.

DETAILED DESCRIPTION

Referring to FIGS. 1-5, a plug valve 10 is illustrated employing a seal assembly 12 for providing a preload between an inlet seal segment 14 and an outlet seal segment 16 against a plug member 18. As explained in further detail below, this preload acts to prevent unwanted particulate and debris such as, for example, sand from frac fluid, from migrating between the plug member 18 and each respective seal segment 14 and 16 during instances of low pressures. Such unwanted particulate and debris causes increased friction thereby limiting movement of the plug valve and reduces seal performance.

Referring specifically to FIG. 1, the plug valve 10 includes a valve body 20 with a central chamber 22 disposed between and connecting an inlet port 24 and an outlet port 26. The inlet seal segment 14 and the outlet seal segment 16 are disposed within the central chamber 22 and each include a bore 14 a and 16 a, respectively, extending therethrough and aligned with an axis 25 of the inlet and outlet ports 24 and 26. As illustrated in FIG. 1, the plug member 18 is disposed within the central chamber 22 and is sandwiched between the inlet and outlet seal segments 14 and 16. The plug member 18 includes a central bore 28 extending therethrough and is movable between an open position, such that the central bore 26 is aligned with the inlet and the outlet ports 24 and 26 to facilitate fluid flow through the plug valve 10, and a closed position, such that the central bore 26 is offset from and blocks the inlet and outlet ports 24 and 26 to prevent fluid flow through the plug valve 10.

Referring specifically to FIGS. 2 and 3, the seal assembly 12 includes the inlet seal segment 14 and the outlet seal segment 16 interlocked together via a pair of side segments 40 and 42 to encircle the plug member 18. The side segments 40 and 42, when interlocked and disposed around the plug member 18, are placed under tension so as to preload and/or otherwise pull the seal segments 14 and 16 inward and against an outer surface 44 of the plug member 18. This preload exists prior to any pressurization of the plug valve 10 and is configured to prevent fluid migration between the outer surface 44 of the plug member 18 and the respective seal segments 14 and 16 when exposed to low pressures. For example, when the valve is in the closed position, fluid pressure from an upstream pressure source (not illustrated) acts on and causes the plug member 18 to drift inside the central chamber 22 and otherwise move into tight metal-to-metal sealing engagement against an inner face 46 of the outlet seal segment 16. As such, a small gap forms between an inner face 48 of the inlet seal segment 14 and the outer surface 44 of the plug member 18. To avoid such gaps, the side segments 42 and 44 act to force or otherwise pull the inlet seal segment 14 into metal-to-metal contact such that the inner face 48 of the inlet seal segment 14 contacts and forms a metal-to-metal seal with the outer surface 44 of the plug member 18. This prevents the migration of fluid and fine particles between the seal segment 14 and the plug member 18. Similarly, when the plug member 18 is in the open position, the side segments 40 and 42 are tensioned to force or otherwise pull both the inlet seal segment 14 and the outlet seal segment 16 into metal to metal contact with the outer surface of the plug member 18 to prevent fluid migration between the plug member 18 and each respective seal segment 14 and 16.

In FIGS. 2 and 3, the inlet and outlet seal segments 14 and 16 and the side segments 40 and 42 each have respective ends that interlock and/or otherwise nest to enable the seal assembly 12 to encircle the plug member 18. The seal assembly 12, when interlocked, forms an inner circular surface 52 having an inner diameter that is sized slightly smaller than an outer diameter of the plug member 18. Accordingly, when the seal assembly 12 is disposed around the plug member 18, the side segments 40 and 42 are stretched and thus, are tensioned to preload and otherwise “pull” the seal segments 14 and 16 inwardly against the outer surface 44 of the plug member 18. According to embodiments disclosed herein, the preload forces generated by the side segments 40 and 42 range from anywhere between, for example, about 445 N (100 lbf) to about 5338 N (1200 lbf), although preload force values outside of this range are also acceptable. For example, in one embodiment, the preload force is a value greater than 5338 N (1200 lbf). In other embodiments, the preload force is in a range greater than zero and less than about 5338 N (1200 lbf). In other embodiments, the preload force is in a range greater than zero and less than about 4895 N (1100 lbf). In other embodiments, the preload force is in a range from less than 445 N (100 lbf) and greater than zero N. In yet other embodiments, the preload forces generated by the side segments 40 and 42 range from anywhere from about 890 N (200 lbf) to about 4893 N (1100 lbf). According to an embodiment disclosed herein, the first and second side segments 42 and 44 are molded from an elastomeric material such as, but not limited to, polyurethane, with sufficient elasticity to provide the preload force.

In the embodiment illustrated in FIGS. 2 and 3, the ends 80 of each of the respective inlet and outlet seal segments 14 and 16 include a groove or a recessed portion 92 that are sized to receive corresponding extensions 90 disposed on each of the ends 82 of the side segments 40 and 42. Thus, when tension is applied to the seal assembly 12, and in particular, to side segments 40 and 42, the seal assembly 12 remains interlocked to prevent separation. As illustrated in FIG. 3, an inner surface 96 of each of the side segments 40 and 42 is spaced apart from the outer surface 44 of the plug member 18 to form a gap G therebetween. Accordingly, by having a gap G, surface-to-surface contact between the side segments 40 and 42 and the plug valve 18 is eliminated, which reduces and can even eliminate any associated friction between the side segments 40 and 42 and the plug valve 18.

In an alternate embodiment, as illustrated in FIGS. 4 and 5 and includes several components given the same reference numerals as provided in FIGS. 1-3, the ends 80 of each of the respective inlet and outlet seal segments 14 and 16 include a shape/configuration that is generally complementary to the shape/configuration of the ends 80 of each of the respective side segments 40 and 42. For example, the ends 82 of side segments 40 and 42 include a groove or pocket 88 and an extension 89 disposed on the inner face 96 of the side segments 40 and 42. The grooves 88 and the extensions 89 are sized and positioned to mate or otherwise nest with the corresponding groove 92 and extension 94 on each of the inlet and outlet seal segments 14 and 16. The grooves 88 and 92 and extensions 89 and 94 are sized so as to nest and interlock the seal assembly 12 together such that, as explained in further detail below, when tension is applied to the seal assembly 12, and in particular, side segments 40 and 42, the seal assembly 12 remains interlocked and will not separate.

According to some embodiments, the ends 80, and 82 optionally include a stiffener or reinforcement mechanism (not illustrated) disposed therein to reduce or eliminate the likelihood of deformation of the ends 80 and 82 when tensile stresses are applied to the side segments 40 and 42. In one embodiment, the stiffener mechanism includes molding the inserts with metal rods, mesh, or plates inside or proximate the ends 80 and 82.

The seal assembly 12 is assembled by accessing the central chamber 22 by removing a cover or cap 100 and inserting the inlet seal segment 14 and the outlet seal segment 16 inside the central chamber 22 proximate the inlet and outlet ports 24 and 26, respectively. The seal segments 14 and 16 are oriented such that the respective bores 14 a and 16 a are coaxially aligned with the inlet and outlet ports 24 and 26. Each seal segment 14 and 16 is secured by one or more pins (not illustrated) to prevent relative lateral movement of the segments 14 and 16 such that the bores 14 a and 16 a remain coaxially aligned with the inlet and outlet ports 24 and 26. Furthermore, in an exemplary embodiment, each seal segment 14 and 16 is sealed to the body preferably by a pair of concentric seals 102 and 104 (FIG. 1) on the seal segments 14 and 16. In yet another embodiment, each inlet and outlet seal segment 14 and 16 is sealed to the plug valve member 18 by at least one concentric seal positioned in grooves located in at least one of the seal segments 14 and 16 and side segments 40 and 42. In other embodiments, at least one of the inlet and outlet seal segments 14 and 16 is sealed to the plug valve member 18 by at least one concentric seal positioned in or on at least one of the seal segments 14 and 16 and side segments 40 and 42. An embodiment provides that the concentric seal may be constructed of an elastomeric or metal material.

Once the seal segments 14 and 16 are positioned within central chamber 22, the side segments are positioned between the ends 80 of the seal segments 14 and 16. In particular, the extensions 90 on the side segments 42 and 44 are aligned with the respective grooves 92 on seal segments 14 and 16 so that the side segments 40 and 42 are nested or otherwise interlocked with the seal segments 14 and 16 to enable the seal assembly 12 to encircle and form a receiving area 106 to frictionally engage the plug member 18. As previously explained, the size of the inner diameter of the seal assembly 12 relative to the outer diameter of the plug member 18 causes the side segments 40 and 42 to deform or otherwise stretch in order to tension the seal assembly 12, and thus pull the seal segments 14 and 16 against the outer surface 44 of the plug valve 18. This creates an inward pulling force to thereby preload the inlet and outlet seal members against the plug 18 to form a seal between the plug and the seal segments 14 and 16 in low pressure conditions to prevent migration of particles therebetween.

In operation, a valve stem is turned by a handle to rotate the plug member 18, between the open and closed positions. In the closed position, the fluid pressure within the central chamber 22 will force the plug member 28 against the outlet seal segment 16 to form a metal-to-metal seal between the plug member 18 and the seal segment 16. This metal-to-metal seal will prevent the fluid in the cavity 18 from migrating between the plug member 18 and the seal segment 16. Furthermore, due to the float between the seal segments and the plug member 18, when the valve is in the open position, the preload on the seal segments 14 and 16 prevents particles in the fluid from migrating between the plug member 18 and the seal segments 14 and 16, thereby facilitating an effective metal-to-metal seal with the downstream seal segment when the valve is closed.

In the foregoing description of certain embodiments, specific terminology has been resorted to for the sake of clarity. However, the disclosure is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes other technical equivalents which operate in a similar manner to accomplish a similar technical purpose. Terms such as “left” and right”, “front” and “rear”, “above” and “below” and the like are used as words of convenience to provide reference points and are not to be construed as limiting terms.

In this specification, the word “comprising” is to be understood in its “open” sense, that is, in the sense of “including”, and thus not limited to its “closed” sense, that is the sense of “consisting only of”. A corresponding meaning is to be attributed to the corresponding words “comprise”, “comprised” and “comprises” where they appear.

In addition, the foregoing describes only some embodiments of the invention(s), and alterations, modifications, additions and/or changes can be made thereto without departing from the scope and spirit of the disclosed embodiments, the embodiments being illustrative and not restrictive.

Furthermore, invention(s) have described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention(s). Also, the various embodiments described above may be implemented in conjunction with other embodiments, e.g., aspects of one embodiment may be combined with aspects of another embodiment to realize yet other embodiments. Further, each independent feature or component of any given assembly may constitute an additional embodiment. 

What is claimed is:
 1. A plug valve comprising: a valve body having an inlet port, an outlet port and a central chamber extending between the inlet port and the outlet port; an inlet seal segment disposed within the central chamber and having a bore extending therethrough and aligned with the inlet port; an outlet seal segment disposed within the central chamber having a bore extending therethrough and aligned with the outlet port; a plug member disposed in the central chamber, the plug member moveable between an open position, to facilitate fluid flow through the plug valve, and a closed position, to block fluid flow through the plug valve; and first and second side segments disposed between and interlocked to the inlet and outlet seal segments to encircle the plug member, the side segments tensioned to preload the seal segments against the plug member to prevent the flow of fluid between the seal segments and the plug member.
 2. The plug valve of claim 1, wherein the inlet and outlet seal segments each include a pair of recesses disposed on an outer face configured to receive corresponding extensions on an inner face of the first and second side segments to interlock the seal segments and the side segments together.
 3. The plug valve of claim 1, wherein the first and second side segments include a pair of recesses disposed on an inner face and configured to receive corresponding extensions on an outer face of the inlet and outlet seal segments.
 4. The plug valve of claim 1, wherein the first and second side segments are formed of urethane.
 5. The plug valve of claim 1, wherein the first and second side segments include an inner arcuate surface, wherein a central section of the inner arcuate surface is spaced apart from the plug member to reduce friction between the plug member and the first and second side sections during movement of the plug member between the open and closed positions.
 6. The plug valve of claim 1, wherein the first and second side segments and the inlet and outlet seal segments form an inner diameter that is sized smaller than an outer diameter of the plug member such that when the seal segments and side segments encircle the plug member, the side segments are tensioned to preload the seal segments against the plug member.
 7. The plug valve of claim 6, wherein the preload force is between about 445 N (100 lbf) to about 2002 N (450 lbf).
 8. The plug valve of claim 6, wherein the preload force is between about 667 N (150 lbf) to about 1780 N (400 lbf).
 9. The plug valve of claim 6, wherein the preload force is between about 1112 N (250 lbf) to about 1557 N (350 lbf).
 10. A plug valve comprising: a valve body having an inlet port, an outlet port and a central chamber extending between the inlet port and the outlet port; an inlet and an outlet seal segment disposed within the central chamber proximate the inlet and outlet ports, respectively, each having a bore extending therethrough and coaxially aligned with valve body inlet and outlet ports; a plug member disposed in the central chamber, the plug member moveable between an open position, to facilitate fluid flow through the plug valve, and a closed position, to block fluid flow through the plug valve; and at least one side segment having ends nestable with respective ends of the inlet and outlet seal segments to interlock the at least one side segment to the inlet and outlet seal segments, the at least one side segment and the seal segments are sized to encircle the plug member such that the at least one side segment is tensioned to preload the seal members against the plug to form a seal between the plug and the seal segments to prevent the flow of fluid between the seal segments and the plug member.
 11. The plug valve of claim 10, wherein the at least one side segment includes a pair of side segments having ends nestable with respective ends of the inlet and outlet seal segments to interlock the side segments to the inlet and outlet seal segments.
 12. The plug valve of claim 10, wherein the inlet and outlet seal segments each include a pair of recesses disposed on an outer face configured to receive corresponding extensions on an inner face of the at least one side segment to interlock the seal segments and the at least one side segment together.
 13. The plug valve of claim 10, wherein the first and second side segments include a pair of recesses disposed on an inner face to receive corresponding extensions on an outer face of the inlet and outlet seal segments.
 14. The plug valve of claim 10, wherein the at least one side segment is formed of urethane.
 15. The plug valve of claim 10, wherein the at least one side segment is tensioned to pull the seal members against the plug with a force of between about 445 N (100 lbf) to about 2002 N (450 lbf).
 16. The plug valve of claim 10, wherein the at least one side segment includes an inner arcuate surface, wherein a central section of the inner arcuate surface is spaced apart from the plug member to form a gap between the at least one side segment and the plug member to reduce friction between the plug member and the at least one side segment during movement of the plug member between the open and closed positions.
 17. The plug valve of claim 10, wherein the at least one side segment and the inlet and outlet seal segments form an inner diameter that is sized smaller than an outer diameter of the plug member such that when the at least one seal side segment and the inlet and outlet seal segments encircle the plug member, the at least one side segment is tensioned to preload the seal segments against the plug member.
 18. A method of manufacturing a plug valve, comprising: forming a valve body having an inlet port, an outlet port and a central chamber extending between the inlet port and the outlet port; inserting an inlet seal segment and an outlet seal segment within the central chamber proximate the inlet and outlet ports, respectively, such that respective bores extending through the inlet and outlet ports are coaxially aligned with valve body inlet and outlet ports; inserting at least one side segment between respective ends of the inlet and outlet seal segments, the at least one side segment having ends nestable with respective ends of the inlet and outlet seal segments to interlock the at least one side segment to the inlet and outlet seal segments, the at least one side segment and the seal segments configured to encircle and form a plug receiving area having an inner diameter; and tensioning the at least one side segment by inserting a plug member having an outer diameter sized larger than the receiving area inner diameter to create a pulling force thereby preloading the inlet and outlet seal members against the plug to form a seal between the plug and the seal segments.
 19. The method of claim 18, wherein inserting the at least one side segment includes inserting a pair of side segments having ends nestable with respective ends of the inlet and outlet seal segments to interlock the side segments to the inlet and outlet seal segments.
 20. The method of claim 19 further comprising: forming extensions on an inner face of the pair of side segments; forming a pair of recesses on an outer face of the inlet and outlet seal segments to receive corresponding extensions on the pair of side segments; and inserting the extensions on the side segments in the recesses on the seal segments to interlock the seal segments and side segments together.
 21. The method of claim 19 further comprising: forming recesses on the pair of side segments; forming extensions on an outer face of the inlet and outlet seal segments for insertion into respective recesses on the pair of side segments; and inserting the extensions in the recesses to interlock the seal segments and side segments together.
 22. The method of claim 18 further comprising forming the at least one side segment of urethane.
 23. The method of claim 18 further comprising forming the plug member diameter a size sufficient to tension the at least one side segment to pull the seal members against the plug member with a force of between about 445 N (100 lbf) to about 2002 N (450 lbf).
 24. The method of claim 18, further comprising forming the at least one side segment to include an inner arcuate surface, wherein a central section of the inner arcuate surface is spaced apart from the plug member to form a gap between the at least one side segment and the plug member to reduce friction between the plug member and the at least one side segment during movement of the plug member between open and closed positions.
 25. A seal assembly for a plug valve including a valve body having an inlet port, an outlet port and a central chamber extending between the inlet port and the outlet port, a plug member disposed in the central chamber, the plug member moveable between an open position, to facilitate fluid flow through the plug valve, and a closed position, to block fluid flow through the plug valve, the seal assembly comprising: an inlet seal segment disposed within the central chamber and having a bore extending therethrough and aligned with the inlet port; an outlet seal segment disposed within the central chamber having a bore extending therethrough and aligned with the outlet port; and first and second side segments having ends nestable with and interlocking to respective ends of the inlet and outlet seal segments for encircling the plug member and tensioning the side segments to pull the seal members against the plug to form a seal between the plug and the seal segments.
 26. The seal assembly of claim 25, wherein the first and second side segments are formed of urethane.
 27. The seal assembly of claim 25, wherein the inlet and outlet seal segments each include a pair of recesses disposed on an outer face configured to receive corresponding extensions on an inner face of the first and second side segments to interlock the seal segments and the side segments together.
 28. The seal assembly of claim 25, wherein the first and second side segments include a pair of recesses disposed on an inner face and configured to receive corresponding extensions on an outer face of the inlet and outlet seal segments to secure the seal segment and the side segments together.
 29. The seal assembly of claim 25, wherein the first and second side segments include an inner arcuate surface, wherein a central section of the inner arcuate surface is spaced apart from the plug member to reduce friction between the plug member and the first and second side sections during movement of the plug member between the open and closed positions.
 30. The seal assembly of claim 29, wherein the first and second side segments and the inlet and outlet seal segments form an inner diameter that is sized smaller than an outer diameter of the plug member such that when the seal segments and side segments encircle the plug member, the side segments are tensioned to preload the seal segments against the plug member.
 31. The seal assembly of claim 30, wherein the preload force is between about 445 N (100 lbf) to about 2002 N (450 lbf). 